Production of coatings



y 16, 1933- P. 5. CASE 1,909,252

I PRODUCTION OF COATINGS Filed Aug. 12, 1929' INVENTOR,

ATTORNEYS.

Patented May 16, 1933 UNITED STATES PATENT OFFICE PHILIP S. CASE, OFNIAGARA FALLS, NEW YORK, ASSIGNOR '10 METALLURGICAL COMPANY, ACORPORATION OF WEST VIRGINIA rnonuo'rron or coArmos Application filedAugust 12, 1929'. Serial No. 385,430.

My invention relates to the production of coatin s of high melting pointmaterials by the aid of the electric arc and especlally to a device forproducing such coatin s.

6 My invention is useful for producing coatings of high melting pointmaterials and particularly easily-oxidized refractory metals and alloys,such as tungsten, ferro-tungsten, and the like. It also may be used toproduce in coatings of other easily oxidized metals such as chromium, orof refractory non-metallic materials such as magnesia. The processconsists broadly in producing an uninterrupted arc, preferably a long orflame-like arc be- 16 tween an electrode and the electrically conductivebody to be coated, and feeding a continuous uniform stream of powderedcoating material onto an area of the body softened or superficiallymelted by the heat of the arc.

The stream of powdered coating material is produced by mixing the powderwith air or other as in definite proportions so as to form a clouc l ormixture capable of being conducted through pipes. This mixture isthickened by 2 extracting a portion of the gas so as to produce a steadystream of mixture of comparatively higher density and of low velocity.The stream is steadily produced and passed into the arc with the volumeand velocity of 30 the gas decreased to a low value so that a materialoxidation of the coating powder or a blowing outof the arc will notresult.

My invention will be more fully understood in connection with thedescription of the 35 drawing constituting a part hereof, in which Figs.1, 2, and 3 are respectfully side, top and end views of my coatingdevice,

Fig. 4 is an enlarged view of a thickener. The coating device isoperated by a handle 40 '1 having an electrically conductive head 2secured thereto by a bolt 3. The head carries an inert electrode ofcarbon or the like and provides a support for a delivery tube to conveythe powdered coating material to the end 4 of the electrode and todirect the material into the zone of the arc. At a suitable distancefrom the end of the handle a split collar 2a is formed in the head 2 anda nipple 4 is clamped in the collar by means of a bolt 5 so that the 50nipple and the electrode attached to the nipple can be adjusted. Theother end of the nipple 4 is screwed into a hollow T shaped member 6.The electrode 7 is inserted into the member 6 and held therein by meansof a threaded wing bolt 8. A bracket 9 for holding the delivery tube 10is screwed into the lateral extension of the T member 6. The extremityof the bracket 9 is formed with a yoke 11 that is provided with a wingbolt 15 which secures the delivery tube 10 in the yoke and providesmeans to remove the tube and to adjust it in vertical and horizontalplanes so that its tip can be positioned. to discharge material near theend of the electrode 7.

An arc is drawn between the electrode 7 on the negative side of the arcand the work or object 16 which is to be coated placed in the electricalcircuit on the positive side of the arc. The work is necessarily anelectrically conductive body and is connected to one terminal of acurrent source 17 through a metallic support 18 and the lead 19. Thelead 19 may be attached to the support by a bolt 20 that is passedthrough an opening in the terminal 21 and the support. The negative sideof the current source 17 is connected to the electrode 7 through thelead 22 which may be bound to the handle 1 by taping 23 which if desiredmay extend the length of the handle to form a smooth grip. The end ofthe lead 22 is secured in electrical contact with the head 2 by a bolt24. The circuit is completed through the head 2, the nipple 4 and a Tmember 6, which latter holds the electrode 7.

The powdered coating material is supplied to the delivery tube 10through an extension tube 25 in the form of a mixture or cloud of gasand powder. This mixture may be produced in any convenient mixingapparatus which will continuously supply a mixture of constant densityand volume. The cloud or mixture is conducted to the extension 25through a pipe 26. In order to conduct the powder through the horizontalor any upwardly inclined portions of the conveyer tubes a large amountof gas is mixed with the powder and this mixture projected through thetube at a high velocity. The volume and velocity of the gas in such astream is so great that it will blow out the electric are or cause it tofluctuate so much that the supply of powder delivered to the arc in thismanner cannot be regulated in proportion to the heat of the arc.Therefore means are provided to reduce the velocity of the stream of themixture and to decrease the volume of the gas inthc stream prior torojecting it into the arc, and to maintain .a steady flow of. coatingpowder into the arc and onto the piece to be coated. These functions areaccomplished with the aid of a thickener 27 placed near the head 2 inthe hue between the extension tube and the delivery tube 10. I

The thickener 27 comprises a series of holes 30 about 34; inch indiameter bored'in the wall of the con'veyer tube and covered by a finescreen or porous sleeve 31 which allows the gas to pass through theholes but retains the powder. The escape of the gas reduces the pressurein the tube and consequently the velocity of the stream and the volumeof gas present in the stream beyond this point. It has been found that awire screen of about 80 meshes to the inch is suitable with a powderwhich passes a screen of 30 meshes and is retained on a screen of meshesto the inch. The best results have been obtained by spacing the holes 30longitudinally along the to walls of the tube on the outside arc of aownwardly bent portion of the tube. By lacing the holes at this pointadvantage is ta en of the fact that the proportion of gas present in thestream of the mixture is greatest along the top wall of the tube andthat the action of avity at this point tends to cause the pow er to fallaway from the screen and prevent the screen from being clogged by thepowder. Also the tube being vertical at this point the coating powder isfed by gravity into the zone of the are without any further need of theaccelerating action of the gas current.

By varying the size and number of the perforations 30 and the finenessof the screen 31, the density and-velocity of the mixture may beregulated at will. The regulation may be fixed by closing the desirednumber of perforations, as by putting sto pers in the perforations 30until the desire regulation is obtained. Temporary regulation may beobtained by placing the hand on the screen over the perforations.

A shield 35 is disposed between the handle 1 and the electrode 7 toprotect the operator from the arc. The shield 35 is attached to theinsulated handle 1 by means of brackets 36 which are bent snugly aroundthe insulated lead 22 and serve to hold the lead in place along thehandle 1.

As a specific example of the operation of my device for building upcoatings, tungsten powder consisting of about 99% tungsten, 0.16% ironand the remainder impurities is taken. The best results are obtainedwith .plied to the extension 25.

powder which passes a standard screen of 30 meshes to the inch and isretained on a standard screen of (i0 meshes to the inch but other sizesof powder may be used. A mixture or dust-cloud consisting of the powderand air is conducted throu h the conduit 26 and sup- This mixture maycontain about 1 part by vohnne of the powder and 800 arts by volume ofair, and for the best results should be supplied as a continuous streamof uniform content of powder and air. In passin through the perforatedarcuatc portion 0 the extension 25, a large proportion of the air ispermitted to escape through the perforations 30 and screen 31. Thediminution in volume or thickening of the mixture together with thechange in direction effected by the curved portion of the extension 25,produces a suspension which may contain for example, 1 part of powderand 7 5 parts of air.

After the powder has passed beyond the thickener 27 the solid particlesare more or less suspended in the remaining air. The stream of powderintermixed with some air flows through the tube 10 by gravity assistedby the momentum of the powder and also slightly assisted by theremaining air. With such a suspension the current of air issuing fromthe delivery tube 10 is reduced to a negligible amount and does not blowout the are or aii'ect the continuous and steady operation of the arc.So long as a continuous and regular supply of the mixture or cloud ofpowder and air is delivered to the extension tube 25 a substantiallyuniform flow of the powder will be delivered to the arc. The characterof the stream issuing from the delivery tube may be changed by changingthe character of the stream delivered to the extension tube 25 and byoperating the thickener as described.

As a specific example of the method of coating with tungsten, aflame-like are two or three inches long is drawn between a carbonelectrode and a steel article upon which the coating is to be formed. Ashallow pool of molten steel appears almost immediately under the arc.The metal powder feed-is then started and the suspension of powder isdirected into the pooL The pool is prompt] covered with the powder andan alloy with the tungsten is formed. As more powder is added, it fusesor-becomes plastic and alloys or amalgamates with the partly molten andplastic surface of the alloyed metal.

To avoid local over-heating or melting of the article, the arc is movedabout over the surface to be coated so that a pool of molten base metalor an area of semi-molten alloy is formed progressively just ahead ofthe stream of powder. With further heating of the allo -coating and withfurther additions of powt er, a coating is built up which grows richerin the constituents of the powder as its thickness increases. Atungsten-containing coating of an inch thick was formed in this way with99% tungsten powder upon a steel base. The coating was perfectly alloyedwith the base and it showed. throughout a perfect union of the tungstenwith the underlying metal. Analysis showed only 6.01/6 iron in thesurface layer of the coating.

The best results are obtained with a long flame-like are butcomparatively short arcs maybe used. Direct current arcs are preferredwith the connections made so that the object to be coated is thepositive electrode. With the above described tungsten powder sus ension,I have obtained the best results wit direct currents of 350 to 500amperes with voltages of 110 to 130. 1

As the small particles of coating material are projected upon the heatedarea, they present the maximum heat absorbing area per unit of volume ofmaterial. The particles become heated to the point of alloying oramalgamating with the material of the object without excessivelypre-heating the objector the powder.. Under the best conditions theaction appears to approximate a momentary fusion or plasticizing of themetal powder and an immediate cooling of the surfaces so that no harmfuloxidation results. The coating action is distinguished from the actionof depositing fused metal from a weld rod or of fusing pellets of metalwhich may be fed into an arc. With the use of pellets or weld rods thematerial to be coated, as well as all of the substance of the rods orpellets must be fused. This necessitates the superheating for aconsiderable length of time of the weld rod material and a seriousexposure to oxidizing conditions results so that deposits free fromoxides are never possible. Such readily oxidized metals as 99% tungstencannot be successfully deposited by fusing rods or pellets.

My invention is not limited to the production of coatings uponconductive materials which are easily fused. Adherent coatings have beensuccessfully formedon other conductive ob]ects, such as graphite.

- I claim:

1. Adevice for producing coatings which comprises a substantially inertelectrode, a tubular delivery member having a discharge to deliver astream-of powdered coating material near one end of the electrode, meansto conduct a cloud-like mixture of powdered.

coating material and gas, and means to extract gas from said'mixture andsupply powand mount said electrode and tubular member, means to conducta cloud-like mixture of powdered coating material and gas, and means toextract gas from said mixture and supply powdered coating material at alow velocity to said delivery member.

3. The combination with an electrode and means to produce an arc betweenthe electrode and a conductive article, of means to conduct a cloud-likemixture of powdered coating material and gas, means to extract gascontinuously from said mixture to produce a continuous thickened streamof powdered coating material, and means to deliver said stream onto anarea of the article which is heated by the are. 4

4:. The combination with an electrode and means to produce an arebetween the electrode and a conductive article, of means to conduct acloud-like mixture of powdered coating material and gas, and a thickenerto extract gas continuously from said mixture, said thickener includinga perforated portion of said conducting means and a porous fine-meshcovering for said perforated portion.

5. The combination with an electrode and means to produce an are betweenthe electrode and a conductive article, of means to conduct a cloud-likemixture of powdered coating material and gas, and athickener to extractgas continuously from said mixture, said thickener including anarcua'tely bent portion of said conducting means having a series ofopenings through the outer peri-' metrical wall of the bent portion andaporous covering for said perforated portion.

In testimony whereof. I afiix my signature.

PHILIP S. CASE.

